Second-home tourism is a very popular form of tourism in many countries, particularly in the Nordic countries. More than half of the Swedish population have access to second homes. Previous studies have revealed that there is great variation between different second homes. Examples range from rustic Australian shacks, lonely cabins in the Norwegian mountains, spacious Swedish archipelago villas and palatial Russian dachas. Still, second homes are often seen and analysed as a unitary category -a perspective that obscures the considerable heterogeneity within the category as well as spatial differences in the impact of second-home tourism. Using a second-home typology from previous research and data on about 660,000 second homes, we analyse the heterogeneity of second homes by mapping the composition of the Swedish second-home stock. Results show the uneven geography of second-home tourism, revealing significant and sometimes steep differences between peripheral areas and urban hinterlands, tourism hotspots, and areas in decline. Based on these results, we assert that there is good cause to move away from using second homes as a unitary category. Instead, we argue for viewing second homes as an umbrella concept with dwelling use in focus. This enables a greater sensibility to place and more accurate analyses of the uneven impacts of second-home tourism. The results also give greater insights into the impact of the 'invisible population' of second-home owners from a public planning perspective. M€ uller, Hall, and Keen (2004)) 提出的第二住宅分类 方法和660000份第二住宅数据, 把瑞典第二住宅的结构绘制在地 图上, 分析了其多样性。结果显示出第二住宅不平衡的地理分布, 揭示出边缘地区、城市腹地、旅游景区和衰落地区明显甚至是尖 锐的差异。基于这些结果, 我们断言这是一个放弃对第二住宅单 一分类的好理由。相反, 我们主张应该从居住用途上把第二住宅

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Second-home tourism is a popular form of tourism in many countries. Sweden has over 600,000 second homes and more than half of the population have access to such properties. Previous literature on second-home tourism indicates that it impacts local communities and municipalities in many different ways, ranging from public services and land-use planning to the housing market and the local economy. However, it has not been sufficiently investigated how, where and by which spatial patterns these impacts might come into effect. Previous research has mostly been in the form of case studies, making generalizations difficult. This paper examines whether a theorized heterogeneity of second-home landscapes transfers into actual spatial variance in the impacts of second-home tourism. The investigation is done through semi-structured interviews with officials from 20 Swedish municipalities, selected using a theoretical model and comprehensive quantitative data. Results reveal considerable variance between different locations and argues for more context-aware second-home research.

The correct description and interpretation of covalent bonding require a quantum mechanical approach. Hückel molecular orbital theory, the simplest quantum mechanical model of molecular electronic structure, is (and in an accompanying online article) shown to be a uniquely useful pedagogical path to the understanding and interpretation of the mechanism of covalent bonding. Using the Hückel model it can be demonstrated that the dynamical character of the molecular orbitals is related simultaneously to the covalent bonding mechanism and to the degree of delocalization of the electron dynamics. The resonance stabilization of conjugated molecules thus corresponds to a special case of the fundamental principle of covalent bonding—the relaxation of dynamical constraints by the delocalization of electronic motion. The covalent bonding mechanism can be seen to arise ultimately from a relaxation of nonergodic constraints on the electron dynamics of the separated atoms leading towards free translation of the valence electrons over two or more atomic centers in a molecule.

The concept of quantum ergodicity and the degree of ergodic behavior reflected by the bound energy eigenstates are studied for some vibrational systems in two and three dimensions. Different approaches are attempted in order to be able to classify and quantify ergodicity in a given system by investigating the energy eigenfunctions. It is argued that the concept of quantum ergodicity is fundamentally connected to the similarity between eigenstates close in energy and to their globality. Previous investigations and definitions of quantum ergodicity can be seen to connect to this theme; they provide different measures of similarity between eigenstates. Here we propose two practical measures to investigate quantum ergodicity. The systems treated include the famous two-dimensional Henon-Heiles and Barbanis systems, which have previously been investigated both classically and quantum mechanically. As a more realistic three-dimensional example, we consider the vibrations of nonrotating NO2 close to dissociation.

Second-home tourism's transformative power on local communities is widely recognized through numerous studies on its social, environmental and economic effects in many parts of the world. A significant share of this literature examines how second-home tourism impacts local housing markets and access to housing. However, few studies have looked into how planning authorities navigate these impacts of second-home tourism and how they differ spatially. Based on previous studies on the heterogeneity of second-home tourism and a comprehensive interview material from 20 Swedish municipalities, this paper examines impacts on local housing markets and the management efforts by local planning authorities. The results show how second-home tourism impact housing markets very differently depending on context when it comes to growth, housing demand and effects for locals' access to housing. The study argues for an acknowledgement of this heterogeneous geography and more context-aware secondhome research that moves beyond the rural-urban dichotomy.

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It is shown that the minimum residual algorithm (MINRES) is able to generate spectral filters sharp enough to obtain bound vibrational eigenstates of NO2 (J=0) by direct access in the most dense part of the spectrum even for the worst near-degeneracy cases. The same is not true for filters constructed as an expansion of the spectral density operator via Chebyshev polynomials. The best performance is obtained in a progressively restarted scheme in which the sharpness of the filter is increased between subsequent restarts to accompany the refinement of the state. Best efficiency and most convenient handling is obtained with early restarts using the Chebyshev-filter, whereas the MINRES-filter is more efficient later in the filtering procedure, where sharp peaking of the filter action is necessary.